1. Field of the Invention
The present invention relates to a non-aqueous electrolyte rechargeable battery, and particularly to an improved safety feature provided to the battery.
2. Description of Related Art
Small, light-weight rechargeable batteries having high energy density are widely used as power source for portable electronic devices. While non-aqueous rechargeable batteries including lithium ion based batteries and lithium ion polymer batteries can output a high voltage, it is essential to ensure that in no circumstances should the batteries let liquid electrolyte leak and, it is desirable that the batteries maintain their high performance even under harsh conditions.
Battery characteristics may deteriorate when the battery is used under a condition exceeding an appropriate range of voltage or temperature. Also, if the battery is subjected to over-charging or left at high temperature, leakage of electrolyte may occur due to a rise in internal pressure. Accordingly, various protective devices for batteries have been proposed.
For example, Japanese Laid-open Patent Application No. 8-185849 proposes a protective device having a shape-memory alloy to shut off the electricity supply from outside of the battery upon an abnormal rise in temperature. Japanese Laid-open Patent Application No. 11-40204 teaches separation of the battery from a charging circuit upon detecting a rise in the internal pressure or temperature of the battery. It also proposes protection of battery from over-charging by the use of a varistor element that operates at a voltage exceeding a predetermined value. Japanese Laid-open Patent Application No. 10-255757 proposes a protective device having a shape-memory alloy to cause short-circuiting across the positive and negative electrodes upon detection of an abnormal rise in the temperature of the battery.
While the protective devices proposed by the above-mentioned Japanese Laid-open Patent Application No. 8-185849 and No. 11-40204 provide safety measures for preventing over-charging of the battery, the battery after the protective device has been operated is in an over-charged state. Thus there remains the risk that leakage of electrolyte may occur or that the battery characteristics may deteriorate.
The protective device disclosed in Japanese Laid-open Patent Application No. 10-255757 prevents over-charging of the battery by causing the battery to discharge, and therefore, the battery is still connected to the charging circuit after the protective device has been operated. Thus there is the risk that the battery may be further charged particularly if large current flows.
The present invention has been devised in view of the above-described problems in prior art, and it is an object of the invention to improve the reliability of non-aqueous electrolyte rechargeable batteries.
To achieve the object, a non-aqueous electrolyte rechargeable battery according to one aspect of the invention includes a switch element provided in a circuit for connecting the battery to an external power source. The switch element is operable in response to a change in temperature of the battery, thereby disconnecting the battery from the circuit and establishing a short circuit across the positive electrode and the negative electrode, the switch element being capable of restoring to its initial state in response to a change in temperature of the battery.
A non-aqueous electrolyte rechargeable battery according to another aspect of the invention includes a closure assembly for closing the open top end of a battery case that is electrically connected to the electrode of first polarity. The closure assembly includes an external terminal, an internal terminal electrically connected to the electrode of second polarity, a switch element in electrical contact with both of the external terminal and the internal terminal, and a ring-like conductive element electrically connected to the battery case and electrically insulated from both of the external terminal and the internal terminal. The switch element disconnects itself from the external terminal and makes electrical contact with the ring-like conductive element in response to a change in temperature of the battery, thereby breaking electrical connection between the battery and an external power source and establishing a short circuit to cause the battery to discharge, the switch element being capable of restoring to its initial state in response to a change in temperature of the battery, thereby re-establishing electrical connection between the battery and the external power source.
These and other objects and characteristics of the present invention will become further clear from the following description with reference to the accompanying drawings.